RED BAG – A Foaling Emergency
Patrick M. McCue
DVM, PhD, Diplomate American College of Theriogenologists
protruding through the vulva within 5 to 10
minutes after the mare breaks her water. As
the mare continues to push, front legs and
then a nose should appear inside the
amnionic sac. The foal is usually delivered
within 15 to 30 minutes after the mare
breaks her water.
The equine placenta consists of an outer
membrane called the chorioallantois, that is
attached to the uterus and an inner
membrane called the amnion, which
surrounds the foal. The chorioallantois is
connected to the uterine wall by millions of
microscopic ‘velcro-like’ attachments called
microcotyledons, except for the area of the
placenta that is in contact with the cervix.
Absence of uterine glands on the cervix
leads to a failure of microcotyledon
development on the adjacent part of the
placenta. Consequently, whereas a majority
of the outer chorionic surface of the placenta
has a brick-red velvety appearance due to
the presence of the microcotyledons, the
region of placenta abutting the cervix lacks
microcotyledons and has a smooth white
appearance. This area is known as the
cervical star. Attachment of the placenta to
the uterus via the microcotyledons is critical
for the transfer of nutrients and oxygen from
the mare across the placenta to the fetus.
Occasionally, a different series of events
occurs during the labor process. Premature
separation of the outer placental membrane
from the uterine wall may lead to protrusion
of the intact fluid-filled chorioallantois
through the vulva. The dark red color of the
outer surface of the chorioallantois gives rise
to common term for premature separation of
the placenta – “redbag”. Confirmation of
the condition may be made by observing the
cervical star on the chorionic surface.
Failure of the outer placental membrane to
rupture during labor and the subsequent
separation of the attachments between the
uterus and placenta lead to a rapid decrease
in oxygen transport to the fetus. As a
consequence, the fetus may suffer from lack
of oxygen (hypoxia) or may die of
asphyxiation if the condition is prolonged or
progresses.
With the onset of labor, the cervix starts to
relax and the uterus begins to contract.
Increased pressure from the uterus causes
the chorioallantois to bulge into the open
cervix. In the normal progression of foaling,
the chorioallantois ruptures at the cervical
star and results in the release of a large
quantity of allantoic fluid (i.e. the “water
breaks”). A thin, transparent, greyish-white
membrane, the amnion, should begin
Owners or foaling personnel must quickly
recognize the red bag condition and
intervene immediately.
The placental
membrane should immediately be opened
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with a sharp instrument such as a knife or
scissors. This will result in a release of
allantoic fluid and a transient delay in
uterine contractions. Veterinary assistance
should be summoned and the foal delivered
as soon as possible. Oxygen should be
administered to the newborn foal if available.
Foals may develop problems associated with
hypoxia even though they may appear to be
normal at birth.
Premature separation of the placenta
accounts for up to 5 to 10% of all cases of
abortion, stillbirth and perinatal death. The
most common causes of red bag are
placental infections, fescue toxicity and
stress. Chronic placental separation from
the uterus may occur over a period of
several days or weeks during late gestation
as a consequence of placentitis.
The
condition may be associated with a cervical
discharge or mild blood loss out the vulva.
A diagnosis of placental separation may be
possible by ultrasound examination of the
pregnant uterus. Recognition of premature
placental separation and appropriate
intervention are the key factors for survival
of the foal.
Amnion protruding through the vulva
Chorioallantoic membrane protruding
through the vulva (Redbag)
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